1. Field of the Invention
The present invention relates to a workpiece surface processing apparatus capable of processing the surface of a workpiece by a plurality of platens and capable of measuring the state of processing of the workpiece.
2. Description of the Related Art
In the past, as an apparatus for processing the surface of a workpiece by a plurality of platens, there has for example been the polishing apparatus such as shown in FIG. 11.
In FIG. 11, reference numeral 100 indicates a platen. Three platens 100 are arranged point symmetrically about a point O. Three holders 101 are provided between these three platens 100.
Due to this, by pressing against and making a donut-shaped wafer W rotate by the three rotating platens 100, the wafer W is polished to a predetermined thickness.
To polish an oxide film of the wafer W to a predetermined thickness by the polishing apparatus, however, it is necessary to monitor the state of polish of the wafer W.
Therefore, in the past, as shown in FIG. 12, a window 201 of a suitable size was made at a predetermined location of a platen 200 and a laser beam was emitted from a laser sensor 210 arranged under the platen 200 through the window 201 to the polished surface of the wafer W to detect the state of polish of the wafer W.
Further, as shown by the two-dot chain line, there is also a technique of arranging the laser sensor 210 down and out from the platen 200 and emit the laser beam to an overhanging projecting portion of the wafer W to detect the state of polish of the wafer W.
With the above related art, however, there were the following problems.
In the polishing apparatus shown in FIG. 11, the wafer W is polished by the rotating platens 100 in a state with the outer peripheral rim of the wafer W held by the holders 101, so it was only possible to polish a wafer W of a donut shape.
That is, when using a disk-shaped wafer W, as shown by the hatching in FIG. 11, since it is not possible to polish the center portion of the wafer W corresponding to the circular region G among the three platens 100, the polishable wafer W ends up being limited to one of a donut shape having a center hole of a size greater than this region G.
As art related to the above polishing apparatus, there are the grinding machine described in Japanese Patent Laid-Open No. 64-11757 and the wafer processing apparatus described in Japanese Patent Laid-Open No. 3-221368, but these apparatuses do not solve the above problem either.
Further, in the technique for measuring the state of polish of the wafer shown in FIG. 12, it is possible to measure the state of polish of the wafer W by the laser beam 210 only when the window 201 of the rotating platen 200 is directly above the laser sensor 210 and the wafer W covers the window 201. Therefore, measurement becomes intermittent and it is difficult to stop the polishing apparatus just when the oxide film of the wafer W has been polished to the optimal thickness. As a result, situations such as excessive polishing or insufficient polishing of the wafer W easily occur. Further, since it is not possible to judge if the portion of the wafer W at the window 201 is a center portion or peripheral portion of the wafer W, it is not possible to measure the state of polish with a high precision.
As opposed to this, in the technique for making the wafer W overhang and measuring the projecting portion by the laser sensor 210, it is possible to judge whether the currently measured location is the peripheral portion or not. Since, however, the amount of overhang is set to be considerably smaller than the radius of the wafer W, it is not possible to measure the center portion of the wafer W. Further, since measurement is possible only when the wafer W is overhanging, this technique also allows only intermittent measurement and therefore like the above art there is the possibility of situations such as excessive polishing or insufficient polishing occurring.